New non-toxic biocompatible dianionic ionic liquids that enhance the solubility of oral drugs from BCS class II

•New non-toxic dianionic ionic liquids were synthesized and characterized.•IC50 higher than 100 mM for fibroblasts L929 cells is achieved for new dianionic ILs.•log P of both drugs decreased in the presence of new dianionic ILs. New dianionic ionic liquids (ILs) based on carboxylic anions and ammonium cations were prepared and characterized. They were used as excipients to increase the solubility of two model oral drugs of BCS class II, ibuprofen and piroxicam. With only 0.2 mol% (≈100 mM) of [N4 1 1 2OH]2[C4H4O4], the solubility increases over 40-fold and 2-fold for ibuprofen, when compared with the parent drug for water and phosphate buffer solution (PBS) 0.01M pH=7.4, respectively. With only 0.02 mol% of [N4 1 1 2OH]2[C4H4O4] it is possible to achieve a water solubility of ≈600 mg/L, in only 5 min at 37°C, corresponding to one dose of ibuprofen that an adult can take. Piroxicam also showed an increase of 20-fold and 1.5-fold for water and PBS respectively, with [N4 1 1 2OH]2[C4H4O4] and [N4 1 1 2OH]2[C5H6O4]. The lipophilicity (logP) of both drugs decreased in the presence of these compounds. The cytotoxicity profile of several of these ILs was determined, and all except [N4 1 1 2OH]2[C3H2O4] have an IC50 higher than 100 mM for fibroblasts L929 cells. [Display omitted]